Airbags have almost become standard equipment in modern motor vehicles. An airbag is a safety device which operates during an emergency such as a vehicle collision and which inflates and deploys under gas pressure to engage with and protect an occupant. Airbags come in various types in accordance with installation locations or applications. For example, a front driver airbag device is provided at a center of a steering wheel in order to protect a driver from a collision in a longitudinal direction (i.e. frontal impact). In addition, in order to protect an occupant from a side collision or from a subsequently occurring rollover (overturn), a curtain airbag device which inflates and deploys along a side window from a vicinity of a ceiling (roof) of a wall part and a side airbag device which inflates and deploys to an immediate side of an occupant from a side part of a seat are provided.
An airbag is provided with a gas generation apparatus called an inflator as a gas supply source. Inflators also come in various types in accordance with types of airbags and installation locations thereof. For example, a disk-type inflator is mainly used for a front driver's side airbag device and the like, while a cylinder-type (cylindrical) inflator is mainly used for a curtain airbag device, a side airbag device, and the like.
For example, Japanese PCT Application No. 2003-501303 describes a side airbag device and a cylinder-type inflator. In the side airbag device, an interior of a cushion is divided into two upper and lower rooms (an upper chamber and a lower chamber) by a panel extending in a vehicle longitudinal direction near a vertical center. The panel is provided with a circulation opening as a hole connecting the two rooms and enables circulation of gas. With the side airbag device according to the above-identified reference, after a tube containing the inflator inflates, gas is first supplied to the lower chamber and subsequently supplied to the upper chamber through the lower chamber.